If wireless technology is so good, why do we still have light switches? We're surrounded by wireless signals, in the form of Wi-Fi and mobile phone networks. We're also surrounded by devices that need controlling, including the TV, the hi-fi, the lights, the door lock and the heating. But the two rarely meet. We could connect all the devices that are currently off the net, but our wireless networks are built wrong.

Switching, slowly

It only takes tiny amounts of data to switch on a light or change TV channels, but our networks are built for speed and range. GSM is being replaced by the faster 3G, and new faster Wi-Fi technologies reach further in our homes. This takes its toll: Wi-Fi and 3G chips are expensive, and need significant electrical power.

What we need is a slow network (because with light switches, you don't need responses in the millisecond range - tenths of a second is enough) that uses very little power.

And around 2003, that technology seemed to have arrived. ZigBee was set to end complicated wiring and give us light switches that can be placed anywhere and controlled from a remote.

Although ZigBee is a short-range connection, it can set up a "mesh" network in which communications can be passed on between remote nodes, so there is no limit to the number of devices in a network, or the distance it can cover in multiple hops if there are enough devices within range of each other.

But where is ZigBee? It's still a marvellous idea, but we aren't all drawing our curtains and turning on the lights with the touch of a button. Worse for the ZigBee community, it has competition.

Alternatives were always possible. ZigBee uses the same unregulated radio spectrum as Wi-Fi and Bluetooth, and a radio communications link, called 802.15.4, defined by the IEEE standards body. Other technologies are lining up to use those resources.

Zensys, for example, uses lower frequencies for Z-Wave, a technology that has had investment from Cisco and Panasonic. Insteon combines wireless and powerline technology, which uses mains wiring to send data. And there's One-Net, an open source alternative that promises to be cheaper.

Another interesting contender uses internet protocol (IP), the hugely successful method that runs the internet and all the corporate networks of the world. But even if ZigBee can shrug off those threats, it's got a bigger one on the horizon: a new version of Bluetooth, the low-power wireless system we all have in our phones.

Bluetooth has always been sparing in its electricity needs, but recently acquired a truly low-power sibling. It's now called "Bluetooth low energy", but was created by Nokia under the name "Wibree" - and last year was adopted by the Bluetooth authorities as an ultra-low power version, sometimes called ULP Bluetooth. In contrast to ZigBee's mesh approach, low-energy Bluetooth is a simplified network - a "star". One device - your phone, say - is the master and the other devices are slaves. ZigBee's fans say this is a big limitation if you want to make something like a burglar alarm for a building.

But backers of low-energy Bluetooth says mesh is not a suitable option for a low-energy network. Slave nodes can just go to sleep when they have nothing to say, but mesh nodes have to be scanning all the time for messages to pass on. "A Bluetooth low-energy device will on average use micro-amps to keep a link up and running," says Robin Heydon, standards architect at chipmaker Cambridge Silicon Radio (CSR). "Mesh requires you to have your receiver on all the time."

And that means problems for the would-be rival. "Low-energy Bluetooth is lower-power, lower-cost and more robust than Zigbee," says Heydon. "It can be added to Bluetooth at virtually zero additional cost." Low-energy Bluetooth can be added very cheaply to a device that already has Bluetooth, such as a phone, because it shares a lot of the circuitry. The biggest cost in a Bluetooth chip is the analogue parts that drive the radio - and low-energy Bluetooth can share these. The only extra costs are some digital parts to handle the Bluetooth low-energy protocol, which cost about 2c (1p). Since it uses the same Bluetooth radio - but more efficiently - adding Bluetooth low energy won't drain phone batteries.

Heile however dismisses low-energy Bluetooth for its lack of features. "It's just Bluetooth with frequency-hopping turned off. That's enough to make a Bluetooth doorlock without the batteries going flat, but it's not a networking solution. It supports no more than eight devices."

That's wrong, says Heydon. "The structure of the network is completely different." Traditional Bluetooth has a limit of eight devices, but the low-energy version's star structure means it can have "a master and many, many, many slaves," he says.

Zigbee backers insist that low-energy Bluetooth's star topology must be inferior to ZigBee's mesh. Meshed devices hand messages on to others, so ZigBee can talk to every device in the house, not just those within 10 metres. Heydon responds: "The problem is, you can't do low power and mesh at the same time."

Painfully and slowly, ZigBee is gaining a foothold. For instance, Gothenberg in Sweden, has commissioned a city-wide scheme to install ZigBee-enabled electricity meters.

Measuring growth

Heile predicts that around 600,000 ZigBee-enabled meters will be installed this year, and analyst West Technology Research Solutions expects 7m ZigBee units to be sold in this year, compared with roughly 2m last year.

Heydon's prediction, though, for ULP Bluetooth is in the billions. "The additional cost of adding low-energy Bluetooth to a Bluetooth chip is very close to zero," he says. From the middle of 2009, "all new phones that have Bluetooth could also have low-energy Bluetooth. That creates an instant market for other devices."

But it's also in the future. Reality brought ZigBee down to earth - could it do the same to low-energy Bluetooth?

Nick Hunn, chief technology officer of the wireless silicon company Ezurio, puts it another way: "The ZigBee PR machine is still running smoothly on bunny power, unaware the headlights are bearing down on it." The next couple of years may decide whether it will get run over - or be the method of choice for turning those lights out.